A NOVEL SIGNALING MECHANISM FOR GENERATING CA2+ OSCILLATIONS AT FERTILIZATION IN MAMMALS

At fertilization in mammals the sperm activates the egg by triggering a series of oscillations in the intracellular free Ca2+ concentration. The precise sequence of events that occur between sperm-egg contact a nd the increases in intracellular Ca2+ remains unknown. Here, we discu ss recent evidence supporting the hypothesis that a cytosolic sperm pr otein enters the egg after gamete membrane fusion and triggers Ca2+ os cillations from within the egg cytoplasm. Biochemical studies suggest that there exists a novel sperm protein, named oscillin, that specific ally comigrates with Ca2+ oscillation-inducing activity. Oscillin has been immunolocalised to the region of the sperm that first fuses with the egg. The concept of a specific protein that triggers Ca2+ oscillat ions may have wider physiological significance since sperm oscillin ca n induce Ca2+ oscillations in somatic cells, such as neurons and hepat ocytes. Unravelling the novel signalling system involved in mammalian fertilization may help reveal some fundamental molecular mechanisms re sponsible for triggering cytoplasmic Ca2+ oscillations.